1. Field of the Invention
The present invention relates to an optical recording/reproducing device, and more particularly, to a method for generating a signal for detecting the direction of movement of a laser spot and detecting the direction of movement of a laser spot, and apparatuses therefor.
2. Description of the Related Art
Track searching of an optical recording/reproducing apparatus means searching for a target track by moving an optical pick-up in the radial direction of a disc. In track searching, it is necessary to determine whether the optical pick-up moves in an intended direction.
Using a conventional method, the direction of movement of a laser spot is detected by the envelope of a sum signal generated by a photodetector. However, in the case of a high density optical disc such as a high-definition DVD (HD-DVD), the width of a track with respect to the size of a laser spot is much smaller than in a conventional CD/DVD. Accordingly, a crosstalk component caused by an adjacent track is mixed with the sum signal. Therefore, it is difficult to detect the envelope of the sum signal.
FIGS. 1A through 1C show changes in a track error signal and an RF signal according to changes in an optical spot and a track width. FIGS. 1A, 1B, and 1C show the track error signals and sum signals when the optical wavelength is 400 nm, the numerical aperture (NA) of an objective lens is 0.6, and track pitches are 0.74 μm (in the case of a DVD), 0.46 μm, and 0.37 μm, respectively.
As shown in FIGS. 1A through 1C, it is difficult to detect the envelope of the sum signal since the track pitch with respect to a uniform optical spot becomes narrower. This is because crosstalk caused by an adjacent track increases due to a narrow track pitch.
Therefore, it is difficult to detect the direction of movement of the laser spot, on the basis of the envelope of the sum signal since the track pitch with respect to the laser spot becomes narrower. This means that it is difficult to detect a track in a high density optical disc.